ahem...
Semi-veteran at this, yet every day I come across something to make me cringe and my ignorance...
I did some episodes of Monty Python to VCD format, where the source was straight-up interlaced NTSC video, 29.97 frames. Conventional wisdom on the forum (and guides) say I should run Inverse Telecine to get it to 24 frames/sec, otherwise I will see lines.
Since I DO see lines on any interlaced source video that I don't convert to forced FILM, I ran it through TMPGEnc's "auto IVTC" function. I just flipped the field from bottom to top, and it did work, and I encoded it and it played nicely at 23.976 frames/sec, 352x240.
OK. I just tried some more episodes, with same interlaced source. This time, I only swapped field order, nothing else but a "sharpen edge" filter. Lo and behold, the encode at 29.97 frames/sec turned out PERFECT. No IVTC!
Is there something about VCD resolutions, or flipping field order, that makes IVTC unnecessary or something?
Please educate me...![]()
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On 2001-08-21 20:27:42, homerpez wrote:
ahem...
I did some episodes of Monty Python to VCD format, where the source was straight-up interlaced NTSC video, 29.97 frames. Conventional wisdom on the forum (and guides) say I should run Inverse Telecine to get it to 24 frames/sec, otherwise I will see lines.
Is there something about VCD resolutions, or flipping field order, that makes IVTC unnecessary or something?
Please educate me...
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Read up on the difference between telecined video and pure interlaced video. If your video isn't telecined, then it makes no sense to do an IVTC before encoding. If your video is interlaced then you may want to deinterlace it before encoding, but when it gets resized to 240 vertical resolution the interlacing artifacts will go away even if you don't since the fields get combined. It's really up to you which looks best.
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I've had this phenomena explained to me at least 50 dozen times by various people, yet I STILL don't fully understand it...
Basically what you're saying is that when I drop down to 352x240 res, I don't have to worry about interlace at all? (Just field order)? Well, seems my last encode proved that one...
So what, then, is the difference between "Telecined" and "Interlaced"? I thought they were the same! Are you talking the difference between "FILM" rate and "NTSC" rate? I know most (if not all) movies on DVD are really 23.976, but they stretch it out to play over 29.97 rate. But actual interlaced NTSC is different from this? UGH.
It hurts my head. I guess if it's straight-up "Interlaced", I'll do the Field order flip, and if it's anything else, just go for "Forced FILM" rate in DVD2AVI. That's worked so far for me... thanks -
A telecine is a device that takes a motion picture film, shot at 24fps, and converts it to 30fps for television display by interpolating 6 new frames each second. When you perform an IVTC you reverse the process, removing the interpolated frames and restoring the film to its original 24fps. There are two advantages for doing this: (1) film is inherently progressive, so restoring the natural framerate eliminates the interlacing and all the artifacts associated with it, and (2) encoding a film at 24fps is equivalent to boosting the bitrate 20%, sharply reducing the occurrence of compression artifacts.
This process only works for film, though. Productions that originate on videotape (news programs, soap operas, sitcoms that claim to be "taped before a studio audience," home camcorder footage) were never, ever anything other than 30fps interlaced. Applying IVTC to these materials is more than likely going to screw them up. You do need to deinterlace these frames for MPEG-1 (and it certainly helps to deinterlace them for MPEG-2 as well) but you can't restore them to 24fps because they never originated on film to begin with.
Now, these are the rules, and there are exceptions to be sure. For example, when an NTSC videotape is converted to PAL for export to Europe, something similar to telecine must be applied in order to reduce our 30fps to their 25fps. This is a complex topic and way beyond the scope of the question, so we'll set it aside except to acknowledge that the rules are never absolute.
<font size=-1>[ This Message was edited by: KoalaBear on 2001-08-22 06:03:21 ]</font> -
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On 2001-08-22 06:00:49, KoalaBear wrote:
Applying IVTC to these materials is more than likely going to screw them up. You do need to deinterlace these frames for MPEG-1 (and it certainly helps to deinterlace them for MPEG-2 as well) but you can't restore them to 24fps because they never originated on film to begin with.
<font size=-1>[ This Message was edited by: KoalaBear on 2001-08-22 06:03:21 ]</font>
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This statement about MPEG-2 isn't really true if you're only going to be watching the resulting stream on a television, because MPEG-2 supports interlaced video.
homerpez: If your source is telecined 24fps then it's best to do an IVTC to get a progressive video stream at the original framerate for encoding to VCD. That's what the forced film option does. If it's 29.97 fps interlaced NTSC video then you could run a deinterlace filter before encoding, but even if you don't you'll loose those interlace artifacts when you reduce the vertical resolution and combine the fields. I have no idea why a field swap would be necessary for what you're doing, and it's probably not.
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How can I tell if my source is 24fps telecine? Wouldn't a 24fps telecine source read as 29.97fps (that's the purpose of the telecine/3:2 pulldown right).
My problem is a lot of my DVDs (Japanese Anime) read as hybrid or film when I preview the VOBs in DVD2AVI. Can I take it that if DVD2AVI says:
a. film = 24fps source that's been telecined to 30fps
b. NTSC = 30fps source, no need to do anything
c. hybrid = combo of the above, should IVTC for 24fps portions
d. film8% or NTSC 89% etc = no idea? I assume like hybird it means so scences are from a 24fps source and others are 30fps. So IVTC is called for.
I still I feel that I am missing someting, but for the record:
1) Movie 24fps progessive
2) DVD is encoded at 24fps w/ telecine to play on 30fps TV, and interlaced (some how?)
3) I rip the DVD VOBs to HD, now because of the telecine the rip will be at 29.97fps
4) I apply IVTC to regenerate the 24fps source
5) I encode to MPEG2
6) I use pulldown to telecine my encode MPEG to 29.97fps so it'll play on my standalone/TV
Because I'm making an MPEG2 which supports interlace, I do not need to deinterlace (but I would/should for MPEG1). Will HD TV solve any of this confusing crap, or just make things worstThanks in advance
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I'm left with 2 things now...
1) A question... say I'm doing 480x480 res SVCD? What should I do about interlacing then? Any way to flip fields in CCE? (or do I need to do more)? (BTW: I flipped feilds the first time, because doing the TMPGEnc "Even-Odd" test, it stuttered the other way)...
2) I think I have an answer on the Anime DVD's, Vejita-sama. Maybe not the real true answer, but... I've run across this on nearly every Anime DVD I've seen, and the answer I've found is simply this.
Run through DVD2AVI under "Forced FILM".
Ignore the "23% NTSC / 77$ FILM" (or whatever) display.
At least on my MPEG-1 encodes, I've never lost frames, seen lines, or had any problems doing it this way.
Again, on SVCD I have no clue what I have to do, but for VCD this works. -
Hoperpez, if you IVTC you don't need to deinterlace as it should generate a progressive video, at leas as well as I understand this whole mess. This is from http://www.inwards.com/~dbb/interlace_myths.html
I'm doing several 'test encodes' now to get the anime working. I'm making the following:
1) Force film off IVTC -> pulldown
2) Force film off, just encoding it
3) Force film on -> pulldown
To see what happens. IVTC is so slow that I'd like to skip it if at all possible. I have a Tbird 1.2Ghz and encode with CCE. I canencode at almost 1x the film run time, but running IVTC takes twice as long to encode, and since I do CCE with multipass=3 that's 8x the run time!!! I could with 4x, but 8x... Maybe I should start looking at a Tbird1.4Ghz
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